A photomultiplier is often optically coupled to a scintillator and incorporated into a well-logging tool to measure radiation within the wellbore. A scintillator crystal emits visible or near-visible light in response to the detected radiation. The photomultiplier receives the light from the scintillator crystal and transforms that light into electrical pulses. The frequency and amplitude of the pulses are related to the radiation measured during well-logging. In the photomultiplier, the electrons are amplified by a linear arrangement of electrodes called dynodes that accelerate and focus the electrons. This linear arrangement of electrodes is termed a venetian blind dynode structure and it is considered to resist the vibration and high heat in well-logging better than other dynode structures, such as a box-type dynode structure.
In the venetian blind dynode structure, the first dynode intercepts about 80% of the incident electrons. Many of the intercepted electrons, however, produce secondary electrons that may be poorly collected by subsequent dynodes.